1. Field of the Invention
The present invention relates to a computer aided design (CAD) system for design operations of a three-dimensional object with the support of a computer to conduct design, expression, manipulation, display and analysis of the three-dimensional object and a method for such support. More particularly, to a computer aided design system for preparing a sketch fundamental plane shape forming a basis for designing a three-dimensional object on a sketch display screen by the utilization of drawing data assets prepared by a two-dimensional CAD, and a method for such support.
2. Description of the Related Art
The purpose of a computer sided design system for carrying out design operations with the support of a computer has conventionally been to prepare two-dimensional drawing data among others. Today, a CAD system is conventionally for transferring to preparation of three-dimensional drawing data for conducting design, expression, manipulation, display and analysis of a three-dimensional object along with the recent innovative improvement of computer performance.
When carrying out design operations of a three-dimensional object on a computer aided design system, it has been the conventional practice to display a sketch screen serving as an operating screen on the display, and conduct three-dimensional modelling of the design object with the use of various support tools on the sketch screen. For three-dimensional modelling, there are available the following two methods. The first method consists of preparing a three-dimensional graphic on the sketch screen as if a sketch were made on a sheet of paper, and the operator repeatedly modifies the three-dimensional graphics on the sketch screen, if necessary repeats consideration. This method is applied when designing an object starting from the very initial step for a new development, for example. The second method is to prepare plane shapes such as end faces and cross-sectional faces of the object forming the basis for three-dimensional modelling while viewing existing drawings, and adding cubic details on the basis of this plane shape. This basic plane shape prepared by the second method is usually called the sketch fundamental plane shape (or sketch sectional shape), and the screen for preparing this basic shape is called the sketch definition screen. The technique of three-dimensional modelling based on such a sketch fundamental plane shape is utilized for changing the model, improvement and upgrading a version of an already designed object, and permits design operations by the effective utilization of the existing drawing data.
In the conventional preparing operation of the sketch fundamental plane shape, however, the operator enters the shape by using the drawing function of the three-dimensional computer aided design system while viewing the existing drawings printed out on sheets of paper. This has posed the problem of the necessity of much time and labor for this input operation when the plane shape is complicated.
There is available a system in which, simultaneously with a window for sketching, two-dimensional drawing data are displayed in another window, and a basic shape is entered into the window for sketching while referring to this window screen. This is, however, similar to the above-mentioned operation in that the operator enters the shape by the use of the drawing function of a three-dimensional CAD system, and imposes a large operational load when entering a complicated plane shape.